This invention relates to an improved form of computer mouse, designed such that the hand position required to manipulate the mouse is a natural xe2x80x9crestingxe2x80x9d position, thus minimizing pain and disability in the hand and wrist.
The hand, when placed on a horizontal surface in front of the body naturally assumes the position wherein the palm is inclined to the horizontal plane typically at an angle from around 50 to 70 degrees. (See FIG. 3) The angle of the hand is measured from the horizontal plane to a line joining the extreme edges of the palm measured from the base of the little finger to the base of the index finger. In this position the fingers are flexed, the thumb (curled) and index finger are opposed and in close proximity (See FIG. 3). The wrist is not pulled backwards (dorsiflexed, see FIG. 1) nor drooped (flexed), nor is it angled to one side or the other (radial/ulnar deviation, see FIG. 2). This position is recognized as a neutral, or natural resting position of the hand by the medical profession. While in this position on a horizontal surface, the hand and forearm can be maintained for long periods without discomfort. It is found that use of the hand which requires prolonged repetitive motion that takes the hand out of this neutral position can cause discomfort and damage. The most widely-known problem of this nature is carpal-tunnel syndrome. Here the bones of the wrist (carpals) form a concavity which is enclosed on the palm side by a ligament (transverse carpal) producing a tunnel through which pass the tendons controlling the fingers and thumb, and the median nerve. It is pressure on the median nerve by thickening of the tendon sheaths, the carpal ligament, or deformation of the bones which causes carpal-tunnel syndrome. Additionally, the muscle which is used to turn the wrist (pronator teres) can also cause compression of the median nerve, simulating carpal-tunnel syndrome.
In particular there are four motions relating to the use of existing mice which contribute strongly to this problem:
Dorsiflexion is where a position is maintained wherein the hand is bent upwards at the wrist, away from the palm (this occurs when the heel of the palm is held on a horizontal surface) which causes severe compression on the median nerve. Typically, the hand has to take on this position in order to manipulate a mouse (See FIG. 1).
Pronation in which the wrist is rotated from the neutral position towards a horizontal position where the palm is approximately parallel to the work surface. Because almost all mouse buttons are relatively flat to the desktop, mouse users must rotate the wrist in order to push a button.
Radial or Ulnar Deviation in which the hand is bent sideways from the wrist either towards the thumb side (radial deviation) or away from the thumb (ulnar deviation). This occurs constantly in mouse manipulation when making fine adjustments to the mouse position (See FIG. 2a-c).
Finger Flexion: the process by which a finger presses down. This causes compression of the median nerve in the wrist. This is the typical action when pressing typical mouse buttons.
In order to fully manipulate the mouse without undue strain, a hierarchy of movement should be possible which allows the whole arm down to the level of the fingertips to be utilized. In order to promote this hierarchy of movement, it should be possible to activate the mouse buttons without having to adjust the position of the hand or fingers, nor to have to hold those parts in a permanently flexed or deviated position. An optimum design for a mouse will therefore support the hand and fingers as they finely control the mouse position while allowing the minimal amount of effort to activate the mouse buttons.
Typical existing mouse designs require the hand to be held with the palm in a horizontal or near horizontal position, which causes the wrist to be twisted (pronation) out of its naturally relaxed position. At the same time the wrist is required to be maintained in a position wherein it is bent backwards (dorsiflexion) to accommodate the volume of the mouse in the hand. Additionally, the typical action of pressing a mouse button requires vertical pressure downwards by the finger which requires leverage of the muscles and tendons of the finger against the wrist. The constant pressing by a fingertip on a mouse button thus puts stress on the entire length of the hand from the fingertip to the wrist.
At the same time, it is observed that in order to precisely manipulate the mouse, the heel of the palm and the articulating part of the wrist is rested on the horizontal support surface. This causes direct compression of the carpal ligament. It also forces lateral movement of the hand (radial or ulnar deviation) to allow fine fingertip control. This lateral movement contributes greatly towards pain and damage to the wrist and hand. Over long periods these required hand motions either singly or in combination can lead to pain and permanent disability. Some mouse designs have attempted to remedy these problems in their design. To correct the problem of pronation, U.S. Pat. No. 5,355,147 by Lear utilizes a ring-shaped device which is gripped vertically in the fist. This has several important faults i.e. that it will not allow the finger-and-thumb manipulation necessary for fine control. It also requires the hand to move out of the neutral position into a vertical position. U.S. Pat. No. 4,862,165 by Gart has curvilinear palmar and thenar support surfaces arranged so that thumb and forefinger are brought close together, but has a mouse button located so that the hand has to be held horizontally requiring dorsiflexion, pronation and lateral wrist movement with all the deleterious results as discussed above. Other variations show some tilting of the hand up to 15 degrees to the horizontal which is insufficient to bring the hand into a neutral position.
Nature did not design Homo Sapiens to be a habitual button pusher. The muscles and tendons of the fingers, hand and wrist can take only so much repetitive stress. Nature did, however, design the hand for squeezing, especially between the thumb and index finger. The muscles and tendons of the thumb have been have been enlarged by nature to take advantage of this action. A mouse design which takes advantage of the enlarged thumb muscles for squeezing will help to relieve overall stress to the hand. A design that also allows use of the mouse while maintaining the neutral position will be more comfortable, be usable for long periods of time, and cause less stress to the wrist and hand. Thus, the need exists for a more natural way of activating buttons that is more sympathetic to the musculature design of the human hand.
The present invention is distinguishable from and an improvement over the relevant prior art by providing a mouse which supports the hand in a neutral position and promotes manipulation and operation of the buttons by a squeezing action using the opposition of thumb and finger. Key objects are as follows:
a. the palmar support surface is tilted at a minimum angle of approximately 35 degrees, and a preferable angle range of 50 to 70 degrees, supporting the hand in a neutral position. In this position the hand can rest on the ulnar side of the heel of the palm, and lateral positioning of the mouse can be achieved by flexion of the wrist in its natural plane of motion. This obviates lateral wrist motion (deviation).
b. the mouse buttons are arranged such that the squeezing action is perpendicular to the plane of the palmar support.
c. the surface of the mouse buttons are concave to direct the squeezing action in opposition to the thumb, and support the fingers in the inclined position.
d. the thumb is supported on a ledge to maintain the neutral hand position
e. the pressure of the thumb is directed horizontally against a gripping surface in opposition to the fingers. This provides a sustainable operation of the buttons and manipulation of the mouse by activating the flexor pollicis brevis and opponens pollicis muscles, causing opposition between thumb and finger (especially the index finger) putting less strain on the tendons in the wrist.
f. a concave surface partially supports the little finger so that slight tilting or movement of the little finger can act to brake or anchor the motion of the hand giving finer control. Thus the mouse can be maneuvered with just the use of thumb and finger.